1. Field of the Invention
This invention relates generally to computer systems and more specifically to an apparatus and method for adjusting operation of a voltage regulator in anticipation of a change in load.
2. Description of the Related Art
In a typical computer system, one or more voltage regulators provide supply voltages to various system components. For example, a first voltage regulator on a motherboard may provide a supply voltage to a central processing unit (CPU) while a second voltage regulator on a graphics card may provide a supply voltage to a graphics processing unit (GPU). Unfortunately, as operating frequencies increase, voltage regulators may struggle to supply enough current when such processing devices rapidly demand additional current.
This may be illustrated by considering the exemplary graphics processing subsystem shown in FIG. 1, in which a voltage regulator 100 provides a supply voltage (VOUT) to a GPU 110. The GPU 110 may utilize a number of high speed processing pipelines operating in parallel to produce high end (realistic) graphical output. When these pipelines are not being heavily used, the current demand of a GPU may be relatively stable. However, when several of these pipelines are loaded up for processing, the resultant switching (of potentially several hundred million transistors) may cause a current demand several times greater than what is demanded when the pipelines are not as heavily loaded.
As illustrated in FIG. 2, a sudden increase in current when the GPU pipelines are heavily loaded (at time T0) may result in a transient drop (spike) in supply voltage, as the current supplied by an output capacitor (or set of capacitors) CO is depleted. As illustrated in FIG. 1, voltage regulators may utilize some type of feedback mechanism, such as a feedback circuit 120 that samples the output voltage and provides a voltage or current feedback signal to the regulator 100. By monitoring this feedback signal and detecting the voltage drop, the regulator can compensate for the drop in voltage by increasing its output, for example, by generating an error signal and using it to increase the duty cycle of a pulse-width-modulated PWM signal used to drive a switching transistor. As a result, after a recovery time (labeled TR0) which may be several milliseconds, the output voltage may recover to at least approach the previous level.
Similarly, when the pipelines are unloaded (at time T1), a sudden decrease in current load may result in a upward transient spike. For some cases, the peak-to-peak magnitude of the transient may be even greater upon release of the load than when the load is increased. In any case, the feedback mechanism may ensure that after a recovery time (labeled TR1) the output voltage may recover to at least approach the previous level.
If these transient voltage spikes cause the supply voltage level to fall below a minimum threshold or exceed a maximum threshold, the GPU may fail, regardless of how quickly the previous voltage level is restored. Unfortunately, by the time the regulator 100 is able to detect the transient voltage changes based on the feedback signal, the output voltage may have changed too much to allow the regulator 100 to adequately compensate. In some cases, the peak-to-peak magnitude of the transient voltage spikes may be controlled with careful selection of components in the regulator circuit. For example, output capacitors CO (typically dominated by rather large “bulk” capacitors) used in the regulator circuit may be chosen with an effective series resistance (ESR) that minimizes peak-to-peak transient magnitudes, while still providing an adequate recovery time. Unfortunately, the size and/or cost penalty of such capacitors tends to be prohibitive.
Accordingly, what is needed is an improved method and apparatus for regulating voltage supplied to integrated circuit devices, such as processing devices (CPUs and GPUs) that exhibit large abrupt changes in current demand.